Microscopic equations of magnetic dynamics with spin-correlations

Abstract Dynamic equations for the average of individual spins are derived for the first time from basic principles. Starting from a Heisenberg ferromagnet with anisotropy in a time-dependent magnetic field, these equations can be regarded as the microscopic analogy to the macroscopic Landau–Lifshitz equations. Apart from the Weiss molecular field, they account for the influence of the spin-correlations. These correlations give rise to the temperature dependence of the dynamic parameters and to the damping of the motion of the spin-system. In addition, they introduce memory effects on how the system was perturbed by the external field. The obtained system of differential equations is convenient for solving boundary problems.